Hi all, so much to reply to! I thank you all for informative replies, which should keep me busy until the next kidney stone hits :(
I'll try to respond to a few here. (1) Absolutely right, Hans, my profuse apologies for a lousy memory in a post done in haste. It was NeilT, while Bill Fothergill's comment seems more in line with what I was suggesting above.
(2) With regard to CO2(eq), actually, I am not calculating (direct) forcing from CO2(eq) at all. I am referring to a Hansen et al paper in which he points out that in past major CO2 rises (55 million and 250 million years ago) the ratio of CO2 rise to global warming appears to be 4 degrees C per doubling, rather than the 2 degrees or so we would expect from CO2 alone. He then conjectures why this might be so -- primarily "other greenhouse gases" and change in albedo. So I am in fact using this to approximate the long-term effect of CO2 rise in the long term, while postulating that much of this will happen in the medium term and that "other greenhouse gas" rise will be proportional to CO2 rise in the medium as well as the long term.
With regard to CO2 Mauna Loa: I am relying on the monthly figures. In these, peak CO2 rise is in April of this year -- yes, I recognize that 1998 peak is different under those measures as well. But if we look at 1999 yearly rise, it has dropped a full 2 ppm to 0.93. Thus, the end point of (as you say) a 9-11 month descent might be about 1 ppm. Personally, given that we are through the bulk of last year's Oct.-Nov. rapid rise, and that Dec.-Feb. were relatively slow-growth months, I'm betting on monthly rise rates well above 3 ppm until Mar., and therefore we will be in the 3.5 ppm ballpark until March (after which, who knows?) Again, this does not strike me as "normal".
I guess what I'm saying in the above is that I am less wrong than you think and we are more in agreement than you think :)

Another month has passed and so here is the updated Arctic sea ice volume graph as calculated by the Pan-Arctic Ice Ocean Modeling and Assimilation System (PIOMAS) at the Polar Science Center: Do you see that 2016 trend line simply refusing to go up, ending at the lowest level on record for th...

3rd comment: Some commenters have noted that the CO2 equivalent of all greenhouse gases now is estimated at 483 ppm plus. I would be careful with that figure, as when we talk about non-CO2 greenhouse gases in 1850 compared to today. So it's not that other greenhouse gases add 78 ppm to the greenhouse effect; it's that they add 78 minus whatever the level of those gases was in 1850. In the case of methane, at least, we know the level was significant in 1850, since today's naturally occurring methane emissions is about equal to man-caused methane emissions (according to a 2007 article quoted in this blog a long while back). I would swag about 2/3 of 78 ppm is the actual rise, or 52 ppm.
However, imho, it is true that as Hansen and others have argued, the net effect of CO2 atmospheric doubling is more like 4 degrees C than 2. We see other greenhouse gases rise in proportion, adding one increment to global warming; we see changes in albedo adding another, by storing more heat at the earth's surface.

Another month has passed and so here is the updated Arctic sea ice volume graph as calculated by the Pan-Arctic Ice Ocean Modeling and Assimilation System (PIOMAS) at the Polar Science Center: Do you see that 2016 trend line simply refusing to go up, ending at the lowest level on record for th...

2nd comment: about the CO2 rise (Mauna Loa) some commenters have noted. Here's a summary excerpt from my blog (waynekernochanblog.blogspot.com): "Let’s start with the CO2 rise that I have been following since early this year. The “baked in” (yearly average) amount of CO2 has reached, effectively, 405 ppm, as of October’s results about 1 ½ years after it passed 400 ppm permanently. More alarmingly, the surge caused at least partly by el Nino is not going away. I have been following CO2 measurements from Mauna Loa for about 5 years, and always before this year the 10-year rate of increase has been a little more than 1.0 ppm per year. The el Nino and follow-on has added almost 3 ppm to that rate, making a rate of almost 1.1 ppm per year. And the new rate of increase shows little signs of stopping, so that we can project a rate of 1.2 ppm within the next 5 years -- a 20 percent increase."
But what is really alarming to me is that the rate of rise of CO2 Mauna Loa has dipped very little after the el Nino ended -- unlike 1998, which saw a sharp drop in rate in 1999 and 2000. This raises the question of whether the "lag time" between CO2 rise and global temp rise is shorter than we thought (i.e., CO2 rise is helping keep global temp rise going) -- at least in these circumstances. And, of course, if the CO2 rise does lead to temp rise sooner rather than later, then the Arctic temps and sea ice will see the greatest impact...

Another month has passed and so here is the updated Arctic sea ice volume graph as calculated by the Pan-Arctic Ice Ocean Modeling and Assimilation System (PIOMAS) at the Polar Science Center: Do you see that 2016 trend line simply refusing to go up, ending at the lowest level on record for th...

I want to delurk to comment on a few things mentioned in this thread. First, Hans thinks that sea level rise will revert to 4 mm/year from the late-2014 to early-2016 10 mm/year.
I question that. It seems to me that melt, and therefore sea level rise, is a function more of the level of global warming (now 1.2 degrees C) rather than the rate of growth of global warming. If you look at 1998 to early 2013, the global temperature level was at least in the same ball park at start and end. Global temps are now far above that, and no one thinks they'll return to the levels of 1998- 2013 again -- especially since CO2 mauna loa continues to rise faster than ever. So I conclude that the "new normal" is likely to be closer to 10 mm/year than 4 mm/year.
Btw, 10 mm/year takes us to just about 3 feet of sea level rise by the end of this century. And does anyone think the rate won't increase?

Another month has passed and so here is the updated Arctic sea ice volume graph as calculated by the Pan-Arctic Ice Ocean Modeling and Assimilation System (PIOMAS) at the Polar Science Center: Do you see that 2016 trend line simply refusing to go up, ending at the lowest level on record for th...

I can't resist delurking to comment on Lord Soth's picture. Does anyone else remember when I got into a heated argument with someone who maintained that North Pole ice would not melt for a long time, if ever? I would guess that his argument was that it was so thick at the North Pole that the melting season was too short to entirely melt it. I think it was in 2012 ...
I know there's a German word (schadenfreude) for feeling pleasure at the sorrows of others. Is there one for feeling happy about being right while sad that it's come to pass?

Another month has passed and so here is the updated Arctic sea ice volume graph as calculated by the Pan-Arctic Ice Ocean Modeling and Assimilation System (PIOMAS) at the Polar Science Center: Weather conditions in the past month - the (Great?) Arctic Cyclone followed by the Mega-Dipole to be ...

@iceman, @neven: thx for the pointers; omrsweetmath's graph is indeed what I'm looking for, although weekly or monthly might make it a little easier to visualize. All agree on long-term volume decreases; using the long-term average tends to mask that trend, while omrsweetmath's version gives some insight into possible "new cycles" and changes in trend after, say, 2012. thx much!

Another month has passed and so here is the updated Arctic sea ice volume graph as calculated by the Pan-Arctic Ice Ocean Modeling and Assimilation System (PIOMAS) at the Polar Science Center: As of May 31st the 2016 trend line is lowest on the graph. A sea ice volume decrease of 3037 km3 duri...

Hi Neven, thx as always :)
A naïve question: I note your observation that "volume is dipping down towards -2 std devs for the first time in a while" (paraphrase). It occurred to me that "decycleizing" the graph around the line might yield some interesting insights. That is, the volume "cycle" means that early in the year the volume is highest above the trend line, in September it's lowest. If one takes an average for the year (more or less) and adds/subtracts deviations from that average from each monthly result, the resulting "smoothed" volume should highlight volume trends more clearly, I would think.
Thoughts? - w

Another month has passed and so here is the updated Arctic sea ice volume graph as calculated by the Pan-Arctic Ice Ocean Modeling and Assimilation System (PIOMAS) at the Polar Science Center: As of May 31st the 2016 trend line is lowest on the graph. A sea ice volume decrease of 3037 km3 duri...

@Chris -- in hopes that you can get back to forecasting rather than wasting your time on Rignot trivia: Joe Romm has been pretty scathing about the NY Times' climate science coverage. I would take anything not written by Justin Gillis, who is imho superb but now mostly writes blog posts on climate change, with a large grain of salt.
My own view is that the piece is written by a relative newbie who is trying to find a "hook" to make it controversial. To take one small example of the inaccuracies, he states that "in the last year a small group of scientists have begun" considering what might happen in terms of greater-than-1-foot-by-2100 sea-level rise with melting glaciers and a few storm surges. (a) scientists have been considering these possibilities for a much longer time, as witness an MIT study that raised the possibility of as much as 10 feet of sea level rise by 2100 several years ago, iirc; (b) it's not storm surges but the increased height of storm surges due to greater energy in the winds of the atmosphere due to increased heat.
I speak as well from personal experience. In the early 1990s as a newly minted computer industry analyst, I happened to receive a call from a Times reporter about a new IBM version of a parallel computer. The reporter desperately wanted to come to one conclusion; I spent a good 15 minutes trying to persuade him that the facts didn't fit, but that there was another noteworthy innovation in parallelism to talk about. When the story came out, I found that he had butchered one of my explanations in order to make it sound like I supported his conclusion. To make it worse, I got loads of congratulations from people who didn't understand the subject matter but assumed that the NY Times must be right.

When I wrote the Beaufort under early pressure blog post last month, I didn't quite expect this unprecedented pressure (timing and magnitude) to keep up for so long. High pressure areas tend to be short-lived in the Arctic, but this one was still going strong when the Beaufort quick update was p...

D and bobcobb: I have to weigh in, as your characterization of Hansen et al. is badly off and possibly disingenuous.
(1) Hansen is not a lone wolf, as you seem to imply. His latest paper has 16 authors, all but 3 clearly climate scientists, who thereby agreed with about what was said in the paper. The paper cites more than 250 research articles as supporting evidence, with at least that many other climate scientists therefore in effect endorsing at least part of the conclusions.
(2) The paper in question does not make "1" prediction about sea level rise. It adduces very good reasons why land-ice melting in Greenland and the Antarctic should be proceeding exponentially (doubling every x years), rather than linearly as in previous models, and tests the likely sea-level rise under 4 cases: doubling every 10, 20, 30, and 40 years. It then notes what is indeed true, that present measurements indicate a doubling "towards the lower end" of the 10-40 span (in fact, best scientific estimates are that Greenland melting is doubling in slightly more than 10 years, the Antarctic in slightly less than 10 years).
(3) Measurement of Greenland melting has been going on and being tested against alternative interpretations for nigh on 4 decades. To say that "no one has a good analog of how Greenland will melt" has nothing to do with Hansen et al. coming up with good reason why we would expect the total melt to be exponential when we are well before a "half-way" melt, and certainly does not make Hansen et al.'s testing of a model with exponential Greenland melting an "assumption".
(4) Hansen et al. did not "attempt to model" the late Eemian (interglacial). They used data from 55 million years ago, 250 million years ago, and the present to come up with a climate model that reflected both trends in global temps and in ocean features that would affect "uptake" by the deep ocean of changes in temps. The late Eemian was then incorporated to verify certain assumptions about how this model would behave in an "intermediate scenario", when atmospheric carbon was 350-400 ppm and there was a rapid spurt in temps -- i.e., increased storms and increased meltwater affecting deep-ocean "uptake".
(5) You say Hansen et al. were "aware" of (criticisms? assumptions?) "but that didn't stop [them] from modeling the scenario." No, they ran the model and found that it reflected measurements of real-world data like ocean temp changes off Antarctica much better than previous models. They also found that it did not yet model some additional features of today's changing climate. Unfortunately, those shortfalls by and large meant that the model almost certainly underestimated the speed of climate change. So what is most likely is that Hansen et al.'s model is too optimistic about the rate of sea level rise.
Finally, let's all remember that this is not about "sea level rise". The last time atmospheric carbon was at 360ppm, the Antarctic was subtropical and most land ice had melted. From every indication of the data points I just cited, that ship has already sailed. The question really is the speed of sea level rise. The uncertainties going forward are effectively the speed which which we add more carbon to the atmosphere, and the actual reaction of the climate to an unprecedentedly rapid human-caused addition of carbon to the atmosphere. The Hansen et al. paper shows that the climate and sea-level rise react more rapidly to the changes in atmospheric carbon than previous models thought, and that the new speed-of-reaction estimate from the model is still very likely to be an under-estimate. That, in turn, means that climate change is going to put a major "burden" on the world economy sooner than we thought, making our cost of "adaptation" greater in the next 85 years and thus the job of "mitigation" that we really need to do immediately that much harder.

When I wrote the Beaufort under early pressure blog post last month, I didn't quite expect this unprecedented pressure (timing and magnitude) to keep up for so long. High pressure areas tend to be short-lived in the Arctic, but this one was still going strong when the Beaufort quick update was p...

It's been a week since I announced that the ice in the Beaufort Sea was going to come under early pressure. Here's a quick update on what has happened so far, how the forecast played out, and what the short-term conditions for this part of the Arctic will be. As expected, the Beaufort Gyre kick...

@Neven thank you for reminding me yet again to keep these things in perspective. You may be amused by the following story:
In the American TV series Get Smart, an agent of the evil organization KAOS is sneaking up on Our Hero with a submarine, intent on nefarious deeds, when the submarine springs a leak. "Should we panic?" asks his henchman. "No!" says the agent in a dreadful German accent. "Ve at KAOS don't panic for just anything, you know."
Later, the level of the water in the submarine has reached their necks. "All right!" announces the agent. "It's time! PREPARE TO PANIC!!!!!"
I have always appreciated your ability to convey when it is indeed time to panic :)

Last month I made a comparison of CryoSat-2 sea ice volume distribution maps for the 2015/2016 Winter analysis, but it was off because the dates didn't exactly match. Better images have emerged during this year's General Assembly of the European Geosciences Union (more on that later this week): ...

I'll weigh in only to add some facts or guesses at facts not discussed last time. The reason afaik that different folks tend to come up with a different "multiple of CO2" value for methane is that when methane is at low levels it has a half-life of about 10 years, while when it is far greater it has a much longer half-life. The reason iirc is that when you have too much methane in the atmosphere, there's not enough oxygen to split off the hydrogen atoms as water (H2O) plus CO2. So a steady level of methane at today's levels may be equivalent to 20 times the effect of an equivalent amount of CO2, while 10 times today's amount might double methane's half-life in the atmosphere and have around 80 times the effect of the equivalent amount of CO2 (these are vague recollections of the CO2 equivalents given at the time, not exact figures).
The question is, how much methane does it take to extend its half-life. Scientists at the time usually tended to believe we were nowhere near the threshold (I hate the term "tipping point"). Moreover, James Hansen et al in a draft paper a couple of years ago found that in the last two episodes of global warming (55 and 155 years ago) methane had a minimal effect. Instead, what supplemented CO2's direct effect were things like black carbon.
Now, there are two things these analyses can't speak to. First, nobody knows just how much of permafrost melt will be released as methane, and how much as CO2. The former is worse in the short term, while the latter is actually worse in the long term (under certain assumptions).
Second, no one really knows how our incredible acceleration of global warming will affect such things as what Neven cited, methane clathrates on the Arctic Ocean seafloor. A study someone cited at the time said flatly that methane clathrates there might melt, but the methane would be released as bubbles (i.e., go directly to the atmosphere) only at a depth of 10-60 feet, and those bubbles would be small (less than 10 meters in diameter. I am skeptical of this conclusion, as the Russian woman scientist who has been reporting Russian sampling over the last few years announced at one that they were seeing bubbles of more than 100 m in diameter in an area that seemed to be more than 100 meters in depth.
My net so far is that methane appears right now to have too many hoops to jump through in order to do more than double, and therefore worrying about methane is probably less important than worrying about carbon emissions, from fossil fuels and the permafrost. But I do hope Neven finds out something new. I still do worry about it.

It's been a week since I announced that the ice in the Beaufort Sea was going to come under early pressure. Here's a quick update on what has happened so far, how the forecast played out, and what the short-term conditions for this part of the Arctic will be. As expected, the Beaufort Gyre kick...

I can speak to the first question, although I can't remember if I read it in Hansen's Storms of My Grandchildren or a Joe Romm post. Rising CO2 is reflected in rising heat that will occur more in winter than summer, more at night than during the day, and more in northern latitudes like the Arctic than near the Equator. It appears that this picture has been complicated recently by research suggesting that the resulting decreased temperature gradient has compromised the strength of the jet stream, leading to colder temperatures from the Arctic driving down more towards the temperate zone and lasting there for a longer time period before a new front arrives.

It's been a week since I announced that the ice in the Beaufort Sea was going to come under early pressure. Here's a quick update on what has happened so far, how the forecast played out, and what the short-term conditions for this part of the Arctic will be. As expected, the Beaufort Gyre kick...

Thx much NeilT, Roger, Bill, and AD -- all very good stuff. I should really bring this back to the Arctic, as Neven has been especially forbearing to let this discussion unrelated to the Beaufort go on this long.
A few final notes that hopefully add to the discussion: (1) There's a fascinating movie under the NOAA site/CO2 emissions showing the spread of fossil-fuel-emission CO2 in the atmosphere from its original ground sources over the period 2011-12. The reason I think it relates is that it shows that strong Chinese emissions are carried by the trade winds across the Pacific in "flares" that occasionally cross Hawaii. It is possible that some of the ML anomalies over the course of a few days, in particular, are caused by intersection with a Chinese (or even Indian) flare. Note also that lesser hot spots in the US East Coast and Western Europe likewise flare across the Atlantic to Western Europe and China, respectively. I can't think why China would have such an outsized effect on ML right now, but it might explain why the ML upsurge has continued for more than a week.
(2)I looked at the four years before and after 1998, and in fact CO2 growth rate was slightly larger before than after. It isn't until 2002 that CO2 growth rate kicks up to a decade-long 2-2.5 ppm/yr average growth rate, from a 1.5-1.9 ppm/yr growth rate before then. And so, given that the first half of this year should show outsized growth rates, I think it will probably be around 2019-2020 that any permanent increase in the growth rate will begin to be clear.
(3) Many of my conclusions about the IEA data are reinforced by my experiences following the computer industry. For example: In the last 10-12 years, there was a massive shift in investment towards "developing countries" at IBM and other places -- primarily China and India, as well as the Philippines to some extent. These could offer much lower labor costs and theoretically a similar product. However, the infrastructure there -- electricity, heating, cooling -- did not have the capacity to support this and did not have the quality/efficiency standards that the US and Europe had. Therefore, the government had to rapidly increase capacity and use the existing inefficient infrastructure as a base with which to do so. To put it in a nutshell: Moving to developing countries showed up as increased profits in global businesses, but also increased CO2 compared to the same investment in developed countries. Moreover, these same businesses found it much more difficult to track their emissions in developing countries. Afaik, that was why, when Microsoft laudably committed to full tracking of its emissions and a goal of carbon neutrality a couple of years ago, it committed only to tracking and neutrality within the US.
Now let me try to relate this back to the Arctic. The CO2 Emissions movie suggests that increases in CO2 at lower latitudes of the NH get transmitted first around the world at those lower latitudes, and then in a somewhat more delayed fashion to upper latitudes, i.e., the Arctic. So I would, as a swag, guess that increased heat over the Arctic due to the trailing edges of el Nino plus ff pollution would not only continue until fall, it might actually intensify, in the Beaufort as elsewhere -- and we might see what happened to temps in Greenland as the result partly of a "flare" from lower latitudes. It is even possible that this will result in an increase in the temperature gradient at the end of this fall, reducing the likelihood of extreme cold in the US/Europe the first part of next winter.

It's been a week since I announced that the ice in the Beaufort Sea was going to come under early pressure. Here's a quick update on what has happened so far, how the forecast played out, and what the short-term conditions for this part of the Arctic will be. As expected, the Beaufort Gyre kick...

It's been a week since I announced that the ice in the Beaufort Sea was going to come under early pressure. Here's a quick update on what has happened so far, how the forecast played out, and what the short-term conditions for this part of the Arctic will be. As expected, the Beaufort Gyre kick...

@Bill: First, thx for the "grok" reference. I must admit that I was a programmer for nearly 13 years before 1990 and never heard it used once. But it did show up in the New Hacker's Dictionary, which is a marvelous read for anyone who can find it.
About the "anomalies": I must admit the scale of the jump last week is unprecedented in my memory, and I've followed CO2 ML since about 2010. Otoh, iirc, both Feb. in the global scale and Mar. in the ML scale showed about a 3.5 ppm increase; so this is clearly above even whatever happened in 1998. I can't rule out some extraneous effects nearby in Hawaii, although why they would surface now and not any other time in recent memory is beyond me.
Re what's causing it: I am trying to write a blog post about it. I view effects from either oceanic upgassing or ocean/land capacity-reaching as less likely. CarbonTracker, I think, attempts to size these effects, and the effects it finds have been pretty stable for the last 15 years at least -- why should both not only change but change sharply at this time?
Yes, the el Nino clearly is having an effect. But why should it have an effect that seems greater than 1998, and why does the effect linger when reports indicate that this el Nino has been no stronger than 1998 at its strongest, and has been weakening for at least 2 1/2 months?
Finally, you have to take into account the fact that our best estimates of fossil-fuel pollution aside from CO2 ML and the like are done by the IEA based on self-reporting by national governments. It takes no conspiracy theory to figure out that the IEA estimates, which report ff pollution as flat over 2014-2015, are probably underestimating the rate of growth of ff-derived atmospheric carbon. Also probably the underestimate is increasing over time.
Part of that self-report is from local governments, part from businesses, and the IEA does not track pollution during production of the fossil fuel. There is a natural tendency for such reporting to capture less as methods change and to avoid the job of reporting. Increased fracking is probably a cause of increased underestimation, since independent studies have shown large amounts of post-wellhead "flaring" (resulting in large methane/CH4 emissions). Heating/electric infrastructure has been shifting away from well-reported Euro and US zones towards China and India, and these also typically have less efficiency in electricity and heat usage than Europe/the US -- it's not clear whether the IEA deals with that problem adequately. NOAA's estimator shows that fossil-fuel pollution's positive carbon-pollution contribution measured at the marine surface grew from 9.14 ppm in 2011 to 9.78 ppm in 2014 -- there doesn't seem to be much of a slowdown in that in 2014.
Putting together all this, if I had to guess, and I do: The IEA figures are wrong. European efforts are having an effect, but are counteracted by increases in China and India -- which are in turn caused primarily by US/Europe business investment. CO2 growth is real, and is caused partly by el Nino, but more by higher ff pollution and by feedback-loop effects in which, for example, exposure of the Arctic translates to increased black carbon on melting snow and possibly heat driven south that makes us use more electricity-based cooling (less efficient than heating).

It's been a week since I announced that the ice in the Beaufort Sea was going to come under early pressure. Here's a quick update on what has happened so far, how the forecast played out, and what the short-term conditions for this part of the Arctic will be. As expected, the Beaufort Gyre kick...

NeilT: It's official. This week's value is 408.69, which is 4.59 ppm above last year at this time, and about 4.5 ppm above the maximum weekly value last year. Afaik, this is the first time the year-to-year increase in weekly ppm has ever topped 1%.

It's been a week since I announced that the ice in the Beaufort Sea was going to come under early pressure. Here's a quick update on what has happened so far, how the forecast played out, and what the short-term conditions for this part of the Arctic will be. As expected, the Beaufort Gyre kick...

NeilT: You should also note that 3 weeks ago the Mauna Loa weekly average hit 405 ppm for the first time ever; last week the average hit 406 for the first time ever; and the first 5 days of this week are averaging about 408.7 ppm, with one day at about 409.4. - w

It's been a week since I announced that the ice in the Beaufort Sea was going to come under early pressure. Here's a quick update on what has happened so far, how the forecast played out, and what the short-term conditions for this part of the Arctic will be. As expected, the Beaufort Gyre kick...

Hopefully this post actually gets through.
Grok was introduced in Heinlein's Stranger in a Strange Land in the late 1960s, meaning (more or less) "to understand deeply and comprehensively." It was then adopted by hippie culture, and from thence moved into computer programming (hacker, in the old, good sense) jargon. It's good to see it again :)

A couple of things were missing from the 2015/2016 winter analysis posted a few days ago, and so I've decided to present them in this separate blog post. Most of these images come from the website of NSIDC research scientist Andrew Slater. Another way to express how warm or not-cold the Arctic ...

Hi Bill,
I would agree with every point you have made. I would even make another: the alternative (non-Mauna Loa) metric tends to show much less fluctuation from year to year, and therefore will probably wind up less than 3.17. However, I will respectfully and with the utmost deference :) disagree with the conclusions you draw.
Extrapolations from limited data are indeed dodgy. Thing is, they are dodgy upwards as well as downwards. In probability terms, there is an equal probability that I am too optimistic about what will happen if we do not make a significant dent in carbon emissions.
Moreover, measured atmospheric carbon is a far more accurate indication of how things are really going than the per-country and global fossil-fuel emissions measurements you cite. To note a couple of examples, in 2009, because of the global economic recession, global measured emissions were down slightly, and have increased at slower rates since, with a net flat result in 2014 and 2015. During that time, carbon emissions increases have gone from the 1s to the 3s. The point is that our measurements do not capture well even the total of fossil-fuel emissions, while atmospheric carbon measurements capture everything.
On a related but minor point: indications are that China's emissions did indeed go down last year, by the most effective method possible: the central authority told regional authorities to cut it out. And India's coal-use expansion is only beginning. And yet, atmospheric carbon increased a lot more than in previous years.
The "physical causative basis" is not easily summarized, and afaik parts of it are not well understood. However, the point of Hansen et al's paper last year (summarized in a post on my blog as well as I could) is that in the past two episodes of global warming, atmospheric carbon increased or decreased at all points in the ratio (4 degrees C per doubling) I have cited, and other existing models have consistently underestimated that change up to a point, because they show "tipping point" or hysteresis behavior that is not there in the data -- they underestimate the effects up to the tipping point.
So this is my long-winded way of saying that yes, atmospheric-carbon data sucks as a method of extrapolation; but it's the best method we have.

Forum member jdallen started speculating about it on the Arctic Sea Ice Forum a few days ago, Robertscribbler then posted a blog about it two days ago, and this was followed by a piece on the Washington Post website yesterday, and today it's mentioned in a Slate article about all the crazy weat...

You are absolutely right. I stated the wrong conclusion from the chain of logic. Because of the lag time between carbon arrival in the atmosphere and the full effects of that arrival, an 8 degrees C rise would happen (assuming, again, continuation of "business as usual"), afaik, in the 2200 to 2300 time frame.
With regard to the Paris climate talks, I share your hope that this marks a significant departure from "business as usual". My concern there is that despite Europe's relative success in achieving rapid decreases in carbon emissions, overall it does not seem to have had a significant effect on "business as usual" global carbon emissions, and therefore whether Paris has a significant effect in the next 10-20 years depends on how much solar displaces oil/coal/natural gas in global transportation and housing over that period. And if it does not do so adequately, we are still on the path of "business as usual" by the only metric that matters -- atmospheric carbon increases.
I should also note, as per Joe Romm, that all estimates, including BAU, do not take into account permafrost melting. My own understanding of Romm's back-of-the-envelope calculation, assuming carbon dioxide rather than methane is the primary emission, is that this would add about 0.6 degrees C in the long run. This is factored into Hansen et al's model, which notes that two previous episodes of carbon atmospheric doubling involving permafrost melting resulted in a 4 degrees C temp increase per doubling.

Forum member jdallen started speculating about it on the Arctic Sea Ice Forum a few days ago, Robertscribbler then posted a blog about it two days ago, and this was followed by a piece on the Washington Post website yesterday, and today it's mentioned in a Slate article about all the crazy weat...

Not sure this is on-topic but:
The initial estimate for the 2015 yearly increase in CO2 as measured from Mauna Loa, Hawaii, is now available. It set a new record for amount of increase: 3.17 ppm. This was the first increase above 3, and was 0.25 above the second biggest increase (1998). It also represented the first time the increase had surpassed 2 in either three or four consecutive years. Increases in 1959-1964 averaged about 0.6 ppm per year, so that in the last 50 years the yearly increase has more than quintupled – a doubling approximately every 20 years.
Projecting forward 40 years, the increase in 2055 would therefore be in the area of 12 ppm, and the total carbon in the atmosphere would be in the 600 ppm range, or more than double the pre-industrial value. Projecting forward another 40 years, the yearly increase would be in the area of 45 ppm, and the total carbon ppm in the atmosphere would be about 1040 ppm, or four times the preindustrial value. Acorrding to the estimate of James Hansen et al that each doubling of CO2 in the atmosphere historically corresponds in the long run to a 4 degrees C (7.2 degrees F) increase in global land temperature, and twice that in the far north/south, We are therefore talking about an increase of 8 degrees C or 15 degrees F from 1850 to 2100 on average and 16 degrees C or 29 degrees F in the far north/south.

Forum member jdallen started speculating about it on the Arctic Sea Ice Forum a few days ago, Robertscribbler then posted a blog about it two days ago, and this was followed by a piece on the Washington Post website yesterday, and today it's mentioned in a Slate article about all the crazy weat...

Andrew Revkin is known for this kind of "your representations of scientific climate-change knowledge are exaggerations because I have my pet scientists" and "let's do something else instead" reporting -- if reporting isn't too kind a word. The Times had a superb climate-science reporter in Justin Gillis but took him off the beat except for occasional blog posts. Notice the bit about "why should they bother to keep fossil fuels in the ground" and the total disregard of folks like Ken Caldeira who have actually looked at these potential technologies.

Everybody wants clean air. We in the West do, the Chinese do, and it'll also be high on the wish list of Indians and people from other developing nations, once their living standards go up. But good things can also have drawbacks. And in this case it could be a drawback that a place like the Arc...

P.S. I just took a look at the November CO2 figures (Mauna Loa). It's an almost unprecedented almost 3 ppm (2.89) increase from Nov. 2014 (the full year of 1998 saw a 2.93 increase, the only comparable full-year figure) -- and afaik that increase has nothing to do with el nino. That's just awful. It's hard not to get sick to my stomach with that one.

Everybody wants clean air. We in the West do, the Chinese do, and it'll also be high on the wish list of Indians and people from other developing nations, once their living standards go up. But good things can also have drawbacks. And in this case it could be a drawback that a place like the Arc...

Hi Neven (et al),
I really should have weighed in earlier -- other matters. James Hansen wrote extensively about the climate-change effects of aerosols in general a few years ago. From memory, this is what he said: increases in aerosols primarily from coal are counteracting (really, slowing) temperature rises due to climate change. However, this is true only as long as aerosol pollution continues to increase. If aerosol pollution levels off, temp rises start to act as if there is no pollution at all. If aerosol pollution decreases, temp rises are faster than the underlying carbon emissions.
As Hansen also noted, there is a limit to how much aerosol pollution people can bear, and therefore at some point in the future people have to start decreasing their aerosol pollution. So all that has happened is that we have been lulled into a false sense that things are better than they are.
A recent article at www.thinkprogress.com/romm/issue details what this means for the Chinese, who are now the primary aerosol polluters. Of particular note is that some of the pollutants can spread halfway around the world, giving Los Angeles an extra day per year of smog.
I would suggest that the Arctic sea ice effects are simply part and parcel of the global effects. Less carbon pollution means more sunlight, heat, and global warming worldwide, not just in the Arctic.
Side notes: According to a recent article in MIT Technology Review, India is caught between a rock and a hard place. To avoid uncontrollable violence, it needs to upgrade living conditions fast in a nation where 9/10 are still at poverty level, and that means coal. They are trying to move to solar as fast as they can, but practically they project increases in coal use for the next 5-10 years at least.
With regard to technologies removing CO2 from the atmosphere, all technical articles I've read agree that deployment of these has been very slow to happen and significant effects of these are not projected for at least 5-10 years, if ever.

Everybody wants clean air. We in the West do, the Chinese do, and it'll also be high on the wish list of Indians and people from other developing nations, once their living standards go up. But good things can also have drawbacks. And in this case it could be a drawback that a place like the Arc...